Being able to test circuits with a multimeter effectively is an essential skill whether you're designing a new project, troubleshooting a faulty device, or just wanting to learn more about electronics.

Read on as we will go over the basic functions and settings of a typical multimeter and show you how to test a circuit board with a  multimeter.

What is a Multimeter

A multimeter is an indispensable test equipment for troubleshooting and measuring electrical circuits. It is a handheld device that can measure voltage, current, and resistance in electrical systems:

● Voltage: The voltage function allows you to measure both alternating current (AC) and direct current (DC) voltage. The DC voltage comes out of batteries, where the current flows in only one direction, while the AC voltage comes from wall outlets, where the current periodically reverses direction.

● Current: The current function lets you measure amperage in AC and DC circuits. Current is the amount of charge flowing through a circuit.

● Resistance: This can be measured in ohms and measures how well a material opposes the flow of current. Resistance functions are helpful for testing continuity and diagnosing faulty components.

In addition to the three basic functions, many multimeters include additional measurement modes. These can include:

● Diode test
● Capacitance measurement
● Frequency counter
● Duty cycle
● Temperature measurement

Digital multimeters display readings on an LCD screen, while analog multimeters feature a meter needle. Most have probes tipped with metal contacts that are safely inserted into circuits for voltage, current, and resistance testing. A multimeter is therefore a versatile tool for circuit board troubleshooting and component-level diagnosis.

How to Test a Circuit Board with a Multimeter

As we've already seen, a multimeter is one of the most basic and useful tools for any technician working with circuit boards. It allows you to troubleshoot issues by checking voltage, continuity, and resistance across components. Following the proper steps is critical to test a circuit board and identify potential problems thoroughly.

Here are the steps to follow when testing a circuit board with a multimeter.

Step #1: Preparation

Before starting any tests, ensure the circuit board is completely disconnected from any power sources. This is important for your safety and to provide accurate readings. Inspect the board for any obvious issues like broken traces, cracked solder joints, or damaged components. Note any locations that may need further examination.

Step #2: Selecting the Proper Measurement Function

Multimeters have different functions for measuring voltage, current, and resistance. The first step is selecting the correct measurement function for the test you want to perform. For basic voltage and resistance checks, use the 20V DC or 200kOhm functions. Higher ranges may be needed depending on specific component values. Take care to set it to the proper direct current (DC) or alternating current (AC) setting.

Step #3: Checking Voltages

Voltage testing is one of the most fundamental evaluations you can do. Probe the power supply points and trace voltage levels through the board. Connect the black probe to common ground and touch the red probe to test points between components and integrated circuits. Nominal voltages should match the schematic. Significant deviations could indicate faulty connections, components, or power delivery issues. Pay close attention to voltage regulators.

Step #4: Measuring Resistances

Set the multimeter to the resistance measurement function to test continuity and resistor values. Touch one probe to each end of a resistor and check that the reading matches the marked value or schematic. You can also check for opens or shorts by probing across circuit sections and verifying negligible or expected resistance levels. Be sure no power is applied during these tests.

Step #5: Testing Components

Discrete components like transistors, capacitors, inductors, and integrated circuits can be probed for opens, shorts, or out-of-tolerance values. Refer to component specifications for expected readings. Low capacitance measurements may indicate a drained or faulty capacitor. Transistors should show resistance in one direction and low to none in the other. Carefully probe ICs and other sensitive devices.

Step #6: Identifying Issues

If voltage levels are too high or low, resistances read as shorts or opens, or component tests reveal abnormalities, you've likely found the source of a problem. Note the location and readings on the board for reference during repairs. Continuing tracing up and down the signal chain can help narrow things down further. Once all issues are identified, the circuit board is fully diagnosed and ready for repairs.

Here is a video guide about how to test a circuit board with a multimeter.

Other Ways to Test a Circuit Board

In addition to using a multimeter, there are other effective methods for testing circuit boards. Here are some alternatives:

In-Circuit Testing

This involves inserting test probes directly into the circuit board while it is still complete and installed in the device. The probes stimulate different points in the circuit to check for electrical continuity and proper resistance values. It allows testing the board and its connections without removing them. Precise robotic probes can be automatically directed by a computer to different points to test even very dense circuitry thoroughly.

Flying Probe Testing

Flying probe testing is like in-circuit testing, only without physical contact. Movable probes are elevated slightly above the board on a gantry system. High-frequency signals are transmitted between the probes and circuit traces. Reflected signals are analyzed by the machine to determine if electrical properties meet specifications. It's helpful in testing bare boards before assembly and doesn't pose a risk of contacting sensitive components.

Automated Optical Inspection (AOI)

A high-resolution camera examines the board through a microscope under different lighting conditions. It captures images and compares them to reference images of a known good board with pattern recognition software. Any deviations in solder joints, placement of components, or missing or excess solder are automatically detected. AOI ensures assembly defects won't cause reliability issues.

X-Ray Inspection

An X-ray machine generates 2D or 3D images of the board's internal structure. It can detect assembly defects not visible externally, such as cold solder joints, missing or misplaced components, bridging between adjacent joints, and cracks in solder. It's usually applied to inspect dense boards where components block direct visual access.

Thermal Imaging

An infrared camera maps temperature variations across the board surface during operation. It can spot components running hotter than expected, indicating a poor connection producing localized heat. 

Visual Inspection

A trained technician examines the board under magnification with good lighting. Although it's the least sophisticated method, the human eye can still spot subtle defects missed by automated inspection, such as dents, scratches, bridging, icicles, and component placement issues. Visual inspection remains a crucial final check after other testing is completed.

Frequently Asked Questions

1) How to Test a Motherboard with a Multimeter

To test a motherboard with a multimeter, first turn off and unplug the computer. Set the multimeter to measure DC voltage, usually indicated by a "V" with a straight line underneath. Touch the positive probe to the 12V rail pin on the motherboard and the negative to the ground. It should read around 12V. You can also test individual components like RAM slots or ports. No voltage means a bad motherboard.

2) What Is the DC Symbol on a Multimeter?

The DC symbol on a multimeter refers to Direct Current. It looks like a "V" with a straight line underneath, as opposed to an AC symbol with a wiggly line. The DC setting measures steady voltages from batteries, power supplies, or circuits that use DC only. It's important to set the multimeter to the correct DC or AC range when taking voltage or resistance measurements.

3) How Do You Find the Short on a Circuit Board with a Multimeter?

To find a short on a circuit board with a multimeter, first inspect the board visually for any burning, bulging, or discolored components. Set the multimeter to continuity/resistance and probe around these areas that power is not reaching as expected. A beeping tone or very low resistance reading indicates a short. You can also disconnect sections of the board one at a time to narrow down the location. The short should be resolved by replacing the faulty components. 

4) How Do You Troubleshoot a Circuit Board?

Basic troubleshooting steps for a circuit board include checking voltages, looking for physical damage, ensuring proper power and ground connections, and testing individual components. Monitor voltages at different points in the circuit, compare the readings to the schematic, and use continuity mode to trace signals and locate breaks or shorts. Look for signs like overheating, bulging capacitors, or discoloration. Narrow it down section by section. If replacing components doesn't fix it, the board may need repair or replacement.

5) How Do I Know If My Circuit Board Is Bad?

The signs of a bad circuit board include smoking/burning smells, physical damage, components that feel hot, incorrect or no voltages present, and intermittent or complete failure of connected devices. If symptoms persist after resetting, reseating connections, and replacing inexpensive components, it usually means the board is faulty and needs repair or replacement, depending on its complexity and cost. A proper diagnosis is needed to confirm.

Conclusion

Testing circuit boards is an important part of the manufacturing and debugging process. A multimeter allows engineers to check for errors or faults during development quickly. 

If you find yourself in need of circuit boards for your next project, consider working with PCBasic. As a leading PCBA manufacturer based in Shenzhen, China, we offer quick turnaround times, competitive prices, and a full range of fabrication and assembly services. Contact us and get started on your design today!